This invention relates to repeater apparatus for amplifying two signals (at the same frequency) in opposite directions, and more particularly, to apparatus for amplifying such signals at microwave frequencies.
In many systems it is a requirement that electrical signals be transmitted in both directions between two locations. The straightforward manner of doing this is to use two separate transmission lines. However, frequently, for economy or other reasons, a single transmission line is used, with the signals transmitted in the two directions at the same time. This usually presents no significant problem, unless amplification is required. In telephony and other arts over the years many arrangements have been used to provide two-way amplification. These systems may include various types of hybrid circuits, fast switching to select the direction of amplification, selective attenuation, negative impedance devices, etc. Problems encountered include singing (oscillation around a loop), imperfect impedance balance at hybrids, echoes, delay distortion effects, phase error, etc.
The state of the art is indicated for example by U.S. Pat. No. 3,689,711 by Earle et al for a Call Diverter Repeater; U.S. Pat. No. 3,855,431 by Stewart for an Electronic Hybrid Amplifier; and U.S. Pat. No. 3,911,372 by Seidel for an Amplifier With Input and Output Impedance Match.
In microwave systems, such as at radar frequencies of one to fifteen gigahertz, it may be particularly important to preserve the phase relation. One prior solution to the two-way amplification problem has been to switch an amplifier to be instantaneously operative in the direction of the signal. This is in effect a time division approach. However, available switches are high speed or high power, but not both.